Prevention op Death by Fertilization 161 



Hence the physico-chemical activation of the unfertilized 

 egg of the sea-urchin consists of two kinds of treatment. The 

 one is a change in the surface of the egg which may or may 

 not result in the so-called formation of the membrane. This 

 change causes the acceleration of oxidations which in my opinion 

 is the essential feature of the process of fertilization. The 

 second treatment consists in abolishing the faulty condition 

 which makes oxidations fatal to the egg. This second treat- 

 ment may consist in exposing the eggs for about half an hour 

 or a little more to a hjrpertonic solution. We can substitute, 

 however, for this treatment another treatment, namely, the 

 deprivation of the egg for three hours from oxidations, either 

 by removing the oxygen from the solution or by adding a trace 

 of potassiiun cyanide to the solution. If, after the treatment 

 with the hypertonic solution for half an hour, or the treat- 

 ment with lack of oxygen for about three hours, the eggs are 

 put back into normal sea-water they can develop into normal 

 larvae. 



We can show that the spermatozoon also causes the develop- 

 ment of the egg by two different agencies comparable in their 

 action to the agencies used in the methods of chemical fertiliza- 

 tion which we have just described. 



For this purpose we must fertilize the egg of the sea-urchin 

 with a sperm different from its own, and for the following 

 reason: The spermatozoon of the sea-urchin enters so rapidly 

 into the egg that it is impossible to show that it causes the 

 development of the egg by two different substances. 



If, however, we fertilize the sea-urchin egg with the sperm 

 of star-fish, it takes from ten to fifty minutes to cause the 

 membrane formation in the eggs, the reason being that the 

 star-fish sperm can penetrate only very slowly into the egg of 

 the sea-urchin. 



It is, as a rule, not possible to fertilize the egg of the sea- 

 urchin by star-fish sperm in normal sea-water. But I found 



